Very high CO2 exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO₂ exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO₂ exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO₂ exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to ?48 μmol CO₂ m^?2 s^?1 and 20 μmol CO₂ m^?2 s^?1, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO₂ uptake was high, the annual budget of ?229 ± 7 ± 49 g C m^?2 y^?1 (±random errors ± systematic errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets indicated that corrections for air density fluctuations were the largest error source (11.3% out of 24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic carbon pool for the uppermost .20 m. These findings have large implications for the perception of the carbon sink/source of Sahelian ecosystems and its response to climate change.     

典型断陷盆地流域生态系统服务价值时空差异研究

以典型断陷盆地——小江流域为研究对象,以1982年的TM影像、2003年的Landsat ETM+影像和2016年的Landsat OLI影像为数据源,结合云南省测绘局所提供的150 000的土地利用状况图,采用 Costanza 公式对生态系统服务价值进行评估,精细刻画出云南小江流域“盆—山”共存的地质分异结构下生态系统服务价值的时空变化特征。结果表明:（1）小江流域以农田生态系统为主,研究期内生态系统格局总体稳定,耕地、建设用地、林地和园地都有不同程度的增加,而未利用地面积减少,水域面积基本不变;（2）1982-2016年,研究区生态系统服务总价值呈上升趋势,1982、2003和2016年生态系统服务总价值分别为90.11×108元、105.65×108元和136.81×108元,耕地、林地、园地和水域的生态系统服务价值整体上升,而未利用地的生态系统服务价值减少;（3）整体上,小江流域南部和东部生态系统服务价值增加明显,而中部和西部地区生态系统服务价值呈阶段性变化或持续下降趋势,小江岩溶河谷区的生态系统服务价值最高,而沉积平坝区的生态系统服务价值密度最低,且为唯一一个衰退型生态系统服务功能区;（4）研究期内小江流域各项生态系统服务价值均呈上升趋势,调节服务居主导地位,且以气候调节服务价值最高。小江流域生态系统服务价值缺乏弹性,水域生态系统面积变化对研究区生态系统价值的变化具有放大作用。实施封山育林、退耕还林、小流域治理工程等石漠化综合治理工程可增加生态系统服务价值。      

Cross-site analysis of perceived ecosystem service benefits in multifunctional landscapes

Rural development policies in many Organization for Economic Co-operation and Development (OECD) member countries promote sustainable landscape management with the intention of providing multiple ecosystem services (ES). Yet, it remains unclear which ES benefits are perceived in different landscapes and by different people. We present an assessment of ES benefits perceived and mapped by residents (n = 2,301) across 13 multifunctional (deep rural to peri-urban) landscapes in Europe. We identify the most intensively perceived ES benefits, their spatial patterns, and the respondent and landscape characteristics that determine ES benefit perception. We find outdoor recreation, aesthetic values and social interactions are the key ES benefits at local scales. Settlement areas are ES benefit hotspots but many benefits are also related to forests, waters and mosaic landscapes. We find some ES benefits (e.g. culture and heritage values) are spatially clustered, while many others (e.g. aesthetic values) are dispersed. ES benefit perception is linked to people’s relationship with and accessibility to a landscape. Our study discusses how a local perspective can contribute to the development of contextualized and socially acceptable policies for sustainable ES management. We also address conceptual confusion in ES framework and present argumentation regarding the links from services to benefits, and from benefits to different types of values.     

The conservation patterns of grassland ecosystem in response to the forage-livestock balance in North China

Being a key ecological security barrier and production base for grassland animal husbandry in China,the balance between grassland forage supply and livestock-carrying pressure in North China directly affects grassland degradation and restoration,thereby impacting grassland ecosystem services.This paper analyzes the spatiotemporal variation in grassland vegetation coverage,forage supply,and the balance between grassland forage supply and livestock-carrying pressure from 2000 to 2015 in North China.We then discuss the spatial pattern of grassland ecological conservation under the impacts of grassland degradation and restoration,and livestock-carrying pressure.Over the last 16 years,the total grassland area in North China decreased by about 16,000 km2,with vegetation coverage degraded by 6.7％ of the grasslands but significantly restored by another 5.4％ of grasslands.The provisioning of forage by natural grassland mainly increased over time,with an annual growth rate of approximately 0.3 kg/ha,but livestock-carrying pressure also increased continuously.The livestock-carrying pressure index without any supplementary feeding reached as high as 3.8.Apart from the potential livestock-carrying capacity in northeastern Inner Mongolia and the central Tibetan Plateau,most regions in North China are currently overloaded.Considering the actual supplementary feeding during the cold season,the livestock-carrying pressure index is about 3.1,with the livestock-carrying pressure mitigated in central and eastern Inner Mongolia.Assuming full supplementary feeding in the cold season,livestock-carrying pressure index will fall to 1.9,with the livestock-carrying pressure alleviated significantly in Inner Mongolia and on the Tibetan Plateau.Finally,we propose different conservation and development strategies to balance grassland ecological conservation and animal husbandry production in different regions of protected areas,pastoral areas,farming-pastoral ecotone,and farming areas,according to the grassland ecological protection patterns.     

Climate change and coral reef bleaching: An ecological assessment of long-term impacts,recovery trends and future outlook

Since the early 1980s, episodes of coral reef bleaching and mortality, due primarily to climate-induced ocean warming, have occurred almost annually in one or more of the world's tropical or subtropical seas. Bleaching is episodic, with the most severe events typically accompanying coupled ocean–atmosphere phenomena, such as the El Niño-Southern Oscillation (ENSO), which result in sustained regional elevations of ocean temperature. Using this extended dataset (25+ years), we review the short- and long-term ecological impacts of coral bleaching on reef ecosystems, and quantitatively synthesize recovery data worldwide. Bleaching episodes have resulted in catastrophic loss of coral cover in some locations, and have changed coral community structure in many others, with a potentially critical influence on the maintenance of biodiversity in the marine tropics. Bleaching has also set the stage for other declines in reef health, such as increases in coral diseases, the breakdown of reef framework by bioeroders, and the loss of critical habitat for associated reef fishes and other biota. Secondary ecological effects, such as the concentration of predators on remnant surviving coral populations, have also accelerated the pace of decline in some areas. Although bleaching severity and recovery have been variable across all spatial scales, some reefs have experienced relatively rapid recovery from severe bleaching impacts. There has been a significant overall recovery of coral cover in the Indian Ocean, where many reefs were devastated by a single large bleaching event in 1998. In contrast, coral cover on western Atlantic reefs has generally continued to decline in response to multiple smaller bleaching events and a diverse set of chronic secondary stressors. No clear trends are apparent in the eastern Pacific, the central-southern-western Pacific or the Arabian Gulf, where some reefs are recovering and others are not. The majority of survivors and new recruits on regenerating and recovering coral reefs have originated from broadcast spawning taxa with a potential for asexual growth, relatively long distance dispersal, successful settlement, rapid growth and a capacity for framework construction. Whether or not affected reefs can continue to function as before will depend on: (1) how much coral cover is lost, and which species are locally extirpated; (2) the ability of remnant and recovering coral communities to adapt or acclimatize to higher temperatures and other climatic factors such as reductions in aragonite saturation state; (3) the changing balance between reef accumulation and bioerosion; and (4) our ability to maintain ecosystem resilience by restoring healthy levels of herbivory, macroalgal cover, and coral recruitment. Bleaching disturbances are likely to become a chronic stress in many reef areas in the coming decades, and coral communities, if they cannot recover quickly enough, are likely to be reduced to their most hardy or adaptable constituents. Some degraded reefs may already be approaching this ecological asymptote, although to date there have not been any global extinctions of individual coral species as a result of bleaching events. Since human populations inhabiting tropical coastal areas derive great value from coral reefs, the degradation of these ecosystems as a result of coral bleaching and its associated impacts is of considerable societal, as well as biological concern. Coral reef conservation strategies now recognize climate change as a principal threat, and are engaged in efforts to allocate conservation activity according to geographic-, taxonomic-, and habitat-specific priorities to maximize coral reef survival. Efforts to forecast and monitor bleaching, involving both remote sensed observations and coupled ocean–atmosphere climate models, are also underway. In addition to these efforts, attempts to minimize and mitigate bleaching impacts on reefs are immediately required. If significant reductions in greenhouse gas emissions can be achieved within the next two to three decades, maximizing coral survivorship during this time may be critical to ensuring healthy reefs can recover in the long term.     

Structure, biomass distribution and trophodynamics of the pelagic ecosystem in the Oyashio region, western subarctic Pacific

Biomass distribution and trophodynamics in the oceanic ecosystem in the Oyashio region are presented and analyzed, combining the seasonal data for plankton and micronekton collected at Site H since 1996 with data for nekton and other animals at higher trophic levels from various sources. The total biomass of biological components including bacteria, phytoplankton, microzooplankton, mesozooplankton, micronekton, fishes/squids and marine birds/mammals was 23 g C m⁻², among which the most dominant component was mesozooplankton (34% of the total), followed by phytoplankton (28%), bacteria (15%) and microzooplankton (protozoans) (14%). The remainder (9%) was largely composed of micronekton and fish/squid. Marine mammals/birds are only a small fraction (0.14%) of the total biomass. Large/medium grazing copepods (Neocalaus spp., Eucalanus bungii and Metridia spp.) accounted for 77% of the mesozooplankton biomass. Based on information about diet composition, predators were assigned broadly into mean trophic level 3–4, and carbon flow through the grazing food chain was established based on the estimated annual production/food consumption balance of each trophic level. From the food chain scheme, ecological efficiencies as high as 24% were calculated for the primary/secondary production and 21% for the secondary/tertiary production. Biomass and production of bacteria were estimated as 1/10 of the respective values for phytoplankton at Site H, but the role of the microbial food chain remains unresolved in the present analysis. As keystone species in the oceanic Oyashio region, Neocalanus spp. are suggested as a vital link between primary production and production of pelagic fishes, mammals and birds.     

广西合浦海草床生态系统服务功能价值评估

海草床生态系统是生物多样性丰富和生产力高的近岸海洋生态系统,本文以广西合浦海草床为例,结合实地调查、已有的研究成果和当地统计资料,综合运用生态经济学、资源经济学等基本理论和方法,对该地区海草生态系统的服务功能进行了价值评估。结果表明2005年该地区海草生态系统的服务功能价值为6．29×105元／a·ha,其中间接利用价值最大,为4．47×105元／a·ha,占总经济价值的70．97％;其次为非利用价值,为1．54x105元／a·ha,占总经济价值的24．52％;最少的是直接利用价值为2．84×104元／a·ha,仅占总经济价值的4．51％。     

海洋溢油污染对生物群落和种群的影响及生态系统的恢复

海洋溢油污染带来的最严重的威胁在于它能够改变或破坏海洋环境中正常存在的生态系统。溢油污染对生态系统的初步影响是造成生物物种多样性、丰度、均匀度下降,进一步则是敏感物种消退,另一些机会物种大量繁殖,群落结构受到扰动。受到溢油污染后的生物群落的变化和恢复过程通常呈现的是多种因素共同作用的结果。溢油作为一种外来的扰动因素,对生态系统的发展强行加注了一种相对统一的发展模式,生态系统会经历一些优势种之间强烈的相互作用,种群数量出现大幅度的波动,系统变得敏感脆弱,生态恢复需要一定的时间。本文对国内外几十年来的研究成果进行综述,总结今后应大力开展海洋石油污染调查研究工作的各个方面。